1. Field of the Invention
This invention generally relates to footwear and more specifically to the structure of foot beds for such footwear and to apparatus and methods for forming such foot beds.
2. Description of Related Art
The stress that athletes place on their bones and muscles during various athletic endeavors has led to a significant body of study. One emphasis has been the interrelationship of footwear and orthopedic problems with some indication that a relationship exists between proper foot support and certain orthopedic problems, particularly those in the lower back. An important aspect of this study has been directed to determining the best position for a foot in footwear, such as in athletic footwear that includes tennis sneakers, running shoes, ski boots, golf shoes and sport walking shoes.
One consequence of these studies is a set of rigorous medical assessments of an individual's foot and lower leg. These assessments require the accumulation of data and measurements that are made while an individual assumes standing, sitting and prone positions. The objective of the data and measurements is to define the structure of a medically acceptable orthotic device. Such assessments are exacting and time consuming. They are subject to errors even when administered by qualified personnel. Moreover, it requires significant time and effort to complete an assessment and then construct an orthotic device. The costs associated with these efforts effectively limits the use of such orthotic devices to individuals who have medical requirements for such devices.
However, a wide range of individuals could benefit from various orthotic devices. Skiers, for example, often spend a significant time in adjusting the fit of their boots by returning to the vendor for the addition of wedges and other items to properly fit the boots to their feet. Runners and other athletes try several different sets of footwear in an attempt to find a pair footwear that "fits" and "feels right". In actuality, these individuals try to find that particular footwear that most closely approximates the proper fit and support for their feet. However, truly custom fitting footwear requires an individual fit for each person's feet to the footwear he or she will wear.
As previously indicated, the costs associated with a medical assessment are prohibitive. The need for developing cost effective foot supports has led to several approaches that attempt to custom fit footwear. Arch supports and wedges are examples of simple items that attempt to fit footwear. More sophisticated approaches include the formation of a molded insole that serves as a platform for a foot, normally replacing the insole supplied with the footwear. U.S. Pat. Nos. 4,139,337; 4,522,777; 4,597,196; 4,669,142; 4,718,179 and 4,803,747 disclose different molded insoles and the apparatus and methods for making such insoles.
In accordance with U.S. Pat. Nos. 4,139,337, an individual stands on a platform with cradles that locate the knees with respect to the feet. Initially, the individual stands on a glass plate so the operator can view the bottom of the feet while guiding the individual to an appropriate reference stance and positioning the knee cradles. Once the stance is obtained and the cradles are adjusted, the individual steps off the stand. An element with a molding face replaces the glass plate. This molding face receives and positions two heated thermoplastic or thermosetting insole blanks. The individual steps onto the insole blanks and assumes the previously determined reference stance. The individual maintains this stance until the insole blanks cool. Then the operator trims the insole blanks to fit inside the individual's footwear.
U.S. Pat. No. 4,522,777 discloses an embodiment of molded insoles. In accordance with this patent, an individual stands on preheated insole blanks that, in turn, are positioned on a specially shaped resilient foam cushion. The individual's feet fully compress a portion of the cushion directly under the balls of the feet. The arch and rear portion of the foot only partially compress the corresponding portions of the cushion. As a result, the ball of each foot is immobile, while the arch and rear portion are mobile and float in the cushion. The cushion has a slight upward slope from back to front that tends to stretch out the toes which in turn tighten the muscles and tendons to make the foot more stable during the molding operation.
In accordance with U.S. Pat. No. 4,597,196, the individual being fitted for a molded insole sits while the operator sizes a three-component blank and heats the components. When the blank is properly heated and assembled, the operator straps the blank to the bottom of the individual's foot and encases the foot and lower leg in a plastic bag. Then the operator draws a vacuum inside the bag apparently so atmospheric pressure on the outside of the bag presses the blank against the bottom of the individual's foot. The operator then positions the foot to lock the midtarsal joint and assists the individual to stand so his or her foot only lightly contacts a mold base. After a few seconds, the individual divides his or her weight equally between both feet, flexes his or her knees and then sits. The operator then lifts the individual's foot and repositions it to lock the midtarsal joint until the insole blank cools and sets.
A molded insole constructed in accordance with U.S. Pat. No. 4,669,142 comprises a one-piece blank that forms to the bottom of the foot. More specifically, an individual stands on compressible foam and assumes a reference position. For example, a skier will assume a downhill skiing position with the knees flexed. The foam forms a negative impression of the individual's foot in its natural position. Then the individual stands on the heated blank that is disposed in the negative impression thereby sandwiching the blank between the individual's foot and the impression while the blank cools. Various abnormalities can be compensated by adding pads to the blank or by positioning of the feet and legs during the molding operation.
U.S. Pat. Nos. 4,718,179 and 4,803,347 disclose custom molded insoles that are a variation of the molded insoles disclosed in U.S. Pat. No. 4,597,196. In this approach a heated blank is strapped to the bottom of a foot and the foot and blank are then encased in a plastic bag. A vacuum is drawn inside the bag allowing the atmospheric pressure to act on the bottom or exterior surfaces of the blank thereby molding it to the bottom of the foot. During this process an operator takes the foot, which is in a non-load bearing condition, and moves the foot until the midtarsal joint locks or nearly locks.
In summary, each of these references discloses a method and apparatus for producing a molded insole for footwear. In each the foot is in either a load-bearing or non-load bearing condition. In each the accuracy of the final mold depends entirely on or at least in a significant part on the skill of the operator in positioning the foot. Further, the prior art apparatus and methods compensate the foot only in one of the sagittal, frontal or transverse planes. It has been recognized, however, that the motion of the foot is complex and that any motion in one plane (e.g., the sagittal plane) produces motion in the other planes (e.g., the frontal and transverse planes). Any device for supporting feet effectively must therefore take into consideration the forces acting on and the motions of the foot in all three planes. In the prior art such compensation has been limited to custom formed foot beds that have been expensive to produce and have required sophisticated personnel in their manufacture.